1. Field of the Invention
This invention generally relates to a system and method for providing a buffer tube and, more particularly, to a system and method for providing a buffer tube that includes a jet that jets fluid against a buffer tube coating.
2. Description of the Related Art
As shown in FIG. 1, in a conventional system for providing a buffer tube, a plurality of optical fibers 10 are pulled through a crosshead 20 by a pulling capstan 30. The crosshead 20 extrudes a buffer tube coating 40 around the optical fibers 10. Then, the buffer tube coating 40 is quickly solidified by pulling the coating 40 (with fibers 10 within the coating 40) through a vat 50 of water. The buffer tube shrinks when it is cooled.
When the coating 40 shrinks, the actual lengths of the optical fibers 10 within the coating 40 become longer than the length of the buffer tube coating 40 that surrounds the fibers 10, and the optical fibers 10 within the buffer tube coating 40 become curved. This extra length is referred to as excess fiber length, or EFL. It is generally desirable to have a small amount of EFL, for example in order to protect the fibers 10 from stress. However, too much EFL is not desirable because it can cause bunching of the fibers 10 within the coating 40 and related attenuation problems.
During manufacturing of the buffer tube, the quick solidification of the coating 40 prevents the coating from shrinking as much as the coating would shrink if it were given more time before solidification. Accordingly, the structure of the coating 40 of a manufactured buffer tube has a built in tendency to shrink.
Before a buffer tube design is used commercially, manufactured buffer tubes of that design are subjected to temperature cycling in order to determine whether they are suitable for field use. This temperature cycling is used to simulate aging of the buffer tubes in a short period of time. For example, the temperature to which the buffer tube is subjected can be cycled between a low temperature of −50 degrees C. and a high temperature of 70 degrees C., or even hotter, for a period of up to two weeks.
However, because the structure of the coating 40 solidifies with a built in tendency toward shrinking, the coating 40 will further shrink when the manufactured buffer tube is subjected to extreme heat during the temperature cycling. This further shrinkage causes the EFL within the buffer tube to increase, which, as discussed above, can cause bunching of the fibers 10 within the coating 40 and related attenuation problems. Therefore, it is desirable to reduce this change in EFL.
FIG. 2 shows a related art system directed at reducing the change in the EFL when the buffer tube is subjected to temperature cycling. In this system, two clenching capstans (or caterpillars) 60 are provided within the vat 50; one of the capstans 60 is provided above the coating 40 and another is provided below the coating 40. The clenching capstans 60 are positioned between the crosshead 20 and pulling capstan 30 because, at this position, the coating 40 is only constrained at one end (i.e., the pulling capstan 30). Therefore, the clenching capstans 60 do not cause tension on any part of the coating system.
The clenching capstans 60 rotate at a velocity that is greater than the velocity of the coating 40 pulled by the capstan 30 and press against the coating 40. Therefore, the structure of the coating 40 is compressed in the downstream region between the clenching captains 60 and the pulling capstan 30 while the coating is cooled. Due to the fact that the structure of the coating 40 is compressed by the clenching capstans 60, the structure of the coating 40 will have a tendency to recoil or expand. However, because the coating 40 solidifies so quickly, the coating's structure does not expand as much as it would if it were given more time before solidification. Accordingly, the structure of the coating 40 will have a built in tendency to expand.
Thus, when the buffer tube is later subjected to temperature cycling, this tendency toward expansion of the coating 40 counteracts the coating's other tendency to shrink. Therefore, the amount of change in EFL is reduced, or eliminated, as compared to that resulting from the FIG. 1 arrangement.
Although the related art system of FIG. 2 does reduce the change in excess fiber length, because the clenching capstan 60 are provided within the vat 50 of water, the capstans 60 must be protected from the water. The system is therefore complex and requires much maintenance, which increases its cost. Moreover, because only two capstans 60 are typically used with the buffer tube 40, the buffer tube 40 of FIG. 2 is not evenly compressed and is instead flattened into an oval shape. Therefore, it would be beneficial to provide a device that provides this compression to the coating 40 in a better, more convenient, and more efficient manner than these clenching capstans 60.